TTHM (Total Trihalomethanes) violations in Oregon
131 active public water systems in Oregon had a TTHM (Total Trihalomethanes) violation in the past three years, 6 of them in the latest quarter of EPA's data. What TTHM (Total Trihalomethanes) is and why it matters.
Systems with a TTHM (Total Trihalomethanes) violation
Latest quarter first, then largest first| System | Serves | Status | Rules violated, 3 yr | Unresolved |
|---|---|---|---|---|
|
Wilsonville, City of Clackamas County |
25,915 | 2 | 0 | |
|
ST Helens, City of Columbia County |
13,410 | 3 | 0 | |
|
Warm Springs Water Treatment Plant Warm Springs · County |
3,800 | 16 | 5 | |
|
Monroe, City of Benton County |
723 | 5 | 1 | |
|
Skyview Acres Water Company Clackamas County |
200 | 4 | 0 | |
|
Guide Dogs for the Blind INC Clackamas County |
75 | 2 | 0 | |
|
Tigard, City of Washington County |
62,500 | 2 | 0 | |
|
Milwaukie, City of Clackamas County |
20,946 | 6 | 1 | |
|
Pendleton, City of Umatilla County |
16,996 | 2 | 0 | |
|
The Dalles, City of Wasco County |
13,010 | 5 | 1 | |
|
Gladstone, City of Clackamas County |
12,121 | 2 | 0 | |
|
Sweet Home, City of Linn County |
10,322 | 4 | 1 | |
|
Hood River, City of Hood River County |
8,577 | 3 | 0 | |
|
Sheridan, City of Yamhill County |
6,494 | 7 | 0 | |
|
Talent, City of Jackson County |
6,293 | 4 | 0 | |
|
Mount Angel, City of Marion County |
3,650 | 3 | 0 | |
|
Nyssa, City of Malheur County |
3,285 | 3 | 0 | |
|
LA Water Co-Op Washington County |
2,500 | 2 | 0 | |
|
Cave Junction, City of Josephine County |
2,160 | 2 | 0 | |
|
North Marion SD #15 Marion County |
2,100 | 2 | 0 | |
|
Clatskanie, City of Columbia County |
2,096 | 5 | 0 | |
|
City of Rainier Columbia County |
1,932 | 8 | 0 | |
|
Brownsville, City of Linn County |
1,906 | 6 | 0 | |
|
Vale, City of Malheur County |
1,837 | 3 | 0 | |
|
Pleasant Home Water District Multnomah County |
1,510 | 2 | 0 | |
|
Colton Water District Clackamas County |
1,500 | 4 | 0 | |
|
Usfs Timberline Lodge 1 Clackamas County |
1,500 | 4 | 0 | |
|
Port of Morrow Morrow County |
1,350 | 4 | 0 | |
|
Lyons Mehama Water District Linn County |
1,300 | 6 | 0 | |
|
Riddle, City of Douglas County |
1,224 | 4 | 0 | |
|
Southwood Park Water District Clackamas County |
900 | 6 | 0 | |
|
Young Life Wasco County |
852 | 2 | 0 | |
|
Prairie City Grant County |
841 | 4 | 0 | |
|
Buell-Red Prairie WD Polk County |
800 | 8 | 0 | |
|
Panther Creek WD Lincoln County |
800 | 5 | 0 | |
|
OR Youth Authority Maclaren Marion County |
750 | 5 | 1 | |
|
Laidlaw Water District Deschutes County |
740 | 2 | 0 | |
|
Mapleton Water District Lane County |
600 | 8 | 0 | |
|
Riverbend Mobile Home Park Clackamas County |
600 | 2 | 0 | |
|
Olney-Walluski Water Assn Clatsop County |
575 | 3 | 0 | |
|
Hiland WC Illahe Golf Club Estates Marion County |
561 | 6 | 0 | |
|
Oceanside Water District Tillamook County |
500 | 3 | 0 | |
|
Mosier, City of Wasco County |
468 | 3 | 1 | |
|
South Prairie Water Assn Tillamook County |
440 | 2 | 1 | |
|
Maupin, City of Wasco County |
420 | 7 | 2 | |
|
Orchard Heights Water Assn Polk County |
381 | 2 | 0 | |
|
Fishhawk Lake Reserve and Community Columbia County |
350 | 6 | 1 | |
|
Sunstone Boulder Creek Lincoln County |
350 | 5 | 0 | |
|
John Day Water District Clatsop County |
350 | 6 | 1 | |
|
Burlington Water District Multnomah County |
340 | 2 | 0 |
About this data
A system is counted once if any of its violations in the past three years involved TTHM (Total Trihalomethanes), including monitoring and reporting lapses. Rules violated and status in the table are for the whole system, not TTHM (Total Trihalomethanes) alone.
Source: the U.S. EPA's Enforcement and Compliance History Online system (ECHO), which publishes the federal Safe Drinking Water Information System. EPA's terms and values are shown as published. The Oregon records are from EPA's data refresh of Oct 7, 2026; EPA refreshes this data quarterly, and states report to EPA with a lag of three to six months, so the newest violations may not appear yet.